Solar collector arrangement

ABSTRACT

A solar collector arrangement comprises at least two solar collectors, each solar collector comprising at least one collector element with at least one flow channel for receiving heat transfer medium to be heated in the solar collector. The at least two solar collectors are arranged in parallel connection relative to each other and the heat transfer medium to be heated in the solar collectors and the heat transfer medium heated in the solar collectors are arranged to flow into the solar collectors and out of the solar collectors in turns one or some solar collectors of the solar collector arrangement at a time.

FIELD OF THE INVENTION

The present invention relates to solar energy and particularly to asolar collector arrangement to be used for collecting solar energy.

BACKGROUND OF THE INVENTION

One type of solar collectors is a solar collector, wherein solar heatenergy received by the solar collector is conducted to heat transfermedium flowing in flow channels in the solar collector. The solarcollectors of that kind are often arranged to form a group of solarcollectors, or a solar collector arrangement, wherein a number oforiginally separate solar collectors are connected in series so that theheat transfer medium is arranged to flow through all the solarcollectors forming the solar collector arrangement.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a novel solar collectorarrangement for collecting solar energy.

The invention is characterized by the features of the independentclaims.

A solar collector arrangement comprises at least two solar collectors,each solar collector comprising at least one collector element with atleast one flow channel for receiving heat transfer medium to be heatedin the solar collector, at least one inflow passage for allowing a flowof the heat transfer medium to be heated into the at least one flowchannel and at least one outflow passage for allowing a flow of heattransfer medium heated in the solar collector out of the at least oneflow channel. The at least two solar collectors in the arrangement arearranged in parallel connection relative to each other and the heattransfer medium to be heated in the solar collectors and the heattransfer medium heated in the solar collectors are arranged to flow intothe solar collectors and out of the solar collectors in turns in a partof the solar collectors at a time.

An advantage of the invention is that the heat transfer medium heated inthe solar collectors may be collected out of the solar collectors onlyone or some solar collectors at a time. The operation of the solarcollector arrangement may thus be controlled only one solar collector orsome solar collectors at a time. There is thus no need to wait until theheat transfer medium in each and every solar collector in the solarcollector arrangement has reached a specific target temperature beforecollecting the heat transfer medium out of the solar collectors. Bydraining the solar collectors in sequence each solar collector spends alarge time in a no-flow state, when heating is accelerated. This way theoutput temperature of the whole collector group is higher than it wouldbe in the case of constant flow.

Some embodiments of the invention are disclosed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail bymeans of preferred embodiments with reference to the accompanyingdrawings, in which

FIG. 1 shows schematically a top view of a solar collector arrangement;

FIG. 2 shows schematically an internal assembly and operation of acontrol unit of the solar collector arrangement; and

FIG. 3 shows schematically a temperature comparison table.

For the sake of clarity, the figures show some embodiments of theinvention in a simplified manner. Like reference numerals identify likeelements in the figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically a top view of a solar collector arrangement1. The solar collector arrangement 1 comprises a number N of solarcollectors 2, FIG. 1 disclosing solar collectors 2 ₁, 2 ₂, . . . , 2_(N-1), 2 _(N). The solar collectors 2 of FIG. 1 comprise a number ofadjacent collector elements 3 between which there may be free spaces 4.The collector elements 3 are intended to receive the solar heat energyand to conduct it to heat transfer medium that is arranged to flowinside the collector elements 3. The collector elements 3 thus form orprovide internal flow channels for the heat transfer medium in the solarcollectors 2 and the heat transfer medium receives the heat energycollected by the collector elements 3 and conveys it forward. Becausethe collector elements 3 are arranged to form flow channels for the heattransfer medium in the solar collectors 2, the same reference sign 3 maybe used in this specification when it is referred either to thecollector element in the solar collector 2 or to the flow channelprovided by the collector element 3. The heat transfer medium may forexample be water or a mixture of water and glycol.

Alternatively to the embodiment shown in FIG. 1 the solar collectors 2and the collector elements 3 therein may be arranged to provide a singleuniform solar collector arrangement structure in view of its mechanicstructure, but wherein solar collectors 2 being operationally separatefrom each other are provided by valves intended to control the flow ofthe heat transfer medium in the solar collector arrangement 1.

The solar collector 2 comprises an inflow passage 5. The inflow passages5 of the solar collectors 2 are connected to a feeding channel 9 of thesolar collector arrangement 1. The feeding channel 9 is intended to feedcool heat transfer medium to be heated into the solar collectors 2through the inflow passages 5 in the solar collectors 2. A direction ofthe flow of the heat transfer medium in the feeding channel 9 is shownin FIG. 1 schematically with an arrow IF. The feeding channel 9 isconnected to a circulation pump 11 that is intended to circulate theheat transfer medium in the solar collector arrangement 1.

The solar collector 2 comprises an outflow passage 6. The outflowpassages 6 of the solar collectors 2 are connected to a dischargechannel 10 of the solar collector arrangement 1. The discharge channel10 is intended to receive the heat transfer medium heated in the solarcollectors 2 through the outflow passages 6 in the solar collectors 2and to forward the heated heat transfer medium to a heat recoveryelement 12. A direction of the flow of the heat transfer medium in thedischarge channel 10 is shown in FIG. 1 schematically with an arrow OF.

The solar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N) are typicallypositioned in somewhat slanted position so that upper ends of the solarcollectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N) connected to the dischargechannel 10 are on a higher position than lower ends of the solarcollectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N) connected to the feedingchannel 9.

The heat recovery element 12 represents a device or a location at whichthe heat energy collected by the solar collectors 2 and conducted intothe heat transfer medium is either stored for later use or istransferred to another system. The heat recovery element 12 may thus beor comprise a heat reservoir or a heat exchanger, for example. The heatrecovery element 12 is not part of the solar collector arrangement 1 butthe solar collector arrangement 1 is connected to the heat recoveryelement 12 via the feeding channel 9 and the discharge channel 10.

Each solar collector 2 comprises in the outflow passage 6 a flow controlvalve 7. An opening of the flow control valve 7 determines a rate offlow of the heated heat transfer medium out of the respective solarcollector 2. An operation of the flow control valve 7, i.e. the openingof the flow control valve 7, is controlled by a respective pilot motor8. The pilot motors 8 of the solar collectors 2 are connected to acontrol unit 13 through a control bus CO8, whereby the pilot motors 8control the opening of the flow control valves 7 in response torespective control commands received from the control unit 13. Thecontrol unit 13 provides a control unit of the solar collectorarrangement 1.

In the solar collector arrangement 1 of FIG. 1 the solar collectors 2are arranged in parallel connection relative to each other so that asingle portion of the heat transfer medium is arranged to becomesupplied and flown through only a single solar collector in the solarcollector arrangement 1, whereby different portions of the heat transfermedium are arranged to become supplied and flown through different solarcollectors 2 in the solar collector arrangement 1. In other words theinflow passages 5 of the solar collectors 2 are arranged in parallelconnection relative to each other and the outflow passages 6 of thesolar collectors 2 are arranged in parallel connection relative to eachother.

When the flow control valve 7 of a specific solar collector 2 is opened,the portion of the heat transfer medium heated in the solar collector 2flows out of the solar collector 2 to the discharge channel 10 throughthe outflow passage 6 in the respective solar collector 2.

The flow of the heat transfer medium out of the solar collector 2 takesplace by the pressure effect provided by the circulation pump 11. Thecirculation pump 11 starts to pump cool heat transfer medium to beheated into the solar collector 2 through the respective inflow passage5 as soon as the heat transfer medium already heated in the solarcollector 2 is started to be collected out of the solar collector 2.This means that cool heat transfer medium to be supplied into the solarcollector 2 forces or pushes the heat transfer medium already being inthe solar collector 2 and heated therein out of the solar collector 2when the flow control valve 7 of the respective solar collector 2 isopened. Cool heat transfer medium is supplied into the solar collector 2as long as the flow control valve 7 is open but is interrupted when theflow control valve 7 is closed. Therefore a separate flow control valvein the inflow passage 5 of the solar collector 2 is not necessarilyneeded. Different possible operation modes of the circulation pump 11and the solar collector arrangement 1 are explained in more detaillater.

The solar collectors 2 in the solar collector arrangement 1 of FIG. 1may be operated so that portion of the heat transfer medium being in thecollector elements 3 of different solar collectors 2 and heated thereinare collected out of the solar collectors 2 in turns one solar collector2 or some solar collectors 2 of the solar collector arrangement 1 at atime. In other words, when a portion of the heat transfer medium beingin the collector elements 3 of a specific solar collector 2 or ofspecific solar collectors 2 and heated therein is collected out of thatspecific solar collector 2 or the specific solar collectors 2, theportions of the heat transfer medium being in the collector elements 3of any other solar collector 2 still remains in the solar collector 2and is prevented to come out of the solar collector 2. This means thatwhen the flow control valve 7 of the specific solar collector 2 or ofthe specific solar collectors 2 is/are open, the portion of the heattransfer medium being in the specific solar collector 2 or in thespecific solar collectors 2 and heated therein is allowed to flow out ofthe specific solar collector 2 or out of the specific solar collectors2, whereas the flow control valves 7 of other solar collectors 2 areclosed, whereby the portions of the heat transfer medium being in theother solar collectors 2 are prevented from flowing out of the othersolar collectors 2.

When the solar collector arrangement 1 of FIG. 1 is introduced, the flowcontrol valves 7 of each solar collector 2 ₁, 2 ₂, . . . , 2 _(N-1), 2_(N) are closed and the circulation pump 11 is turned on and is operatedfor supplying cool heat transfer medium to the solar collectorarrangement 1 as long as a heat transfer circuit provided by all thesolar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N), the feeding channel9, the discharge channel 10 and appropriate parts in the heat recoveryelement 12 are full of the heat transfer medium.

According to an embodiment the circulation pump 11 and the solarcollector arrangement 1 are operated intermittently, either betweenfixed or adjustable time periods. In this embodiment, when a certainperiod of time has elapsed after introducing the solar collectorarrangement 1 as disclosed in the preceding paragraph, the portions ofthe heat transfer medium heated in the solar collectors 2 ₁, 2 ₂, . . ., 2 _(N-1), 2 _(N) are started to be collected out of the solarcollectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N) one solar collector orsome solar collectors at a time. This means, for example, that the flowcontrol valve 7 in the outflow passage 6 of the first solar collector 2₁ is opened as controlled by the control unit 13 through the control busCO8 and the respective pilot motor 8. At the same time the control unit13 controls, through a control line CL11, the circulation pump 11 toturn on and start to operate, whereby the portion of the heat transfermedium being in the first solar collector 2 ₁ and heated therein startsto flow out of the first solar collector 2 ₁ to the discharge channel 10through the respective outflow passage 6 and a portion of cool heattransfer medium to be heated is supplied from the feeding channel 9 tothe first solar collector 2 ₁ through the respective inflow passage 5.After all of the portion of the heat transfer medium heated in the firstsolar collector 2 ₁ has been collected out of the first solar collector2 ₁, the flow control valve 7 in the outflow passage 6 of the firstsolar collector 2 ₁ is closed as controlled by the control unit 13through the control bus CO8 and the respective pilot motor 8. Thecirculation pump 11 may be on all the time but the pressure provided bythe circulation pump 11 is dimensioned such that it does not cause theflow of the heat transfer medium out of the solar collector 2 unless theflow control valve 7 is opened.

For verifying that all of the portion of the heat transfer medium heatedin the first solar collector 2 ₁ has been collected out of the firstsolar collector 2 ₁, there is in the feeding channel 9 a flow indicator14 for indicating an amount or a measure V_(MEAS) of the heat transfermedium supplied by the circulation pump 11, which measure VM_(EAS) iscompared in the control unit 13 to a calculated or determined heattransfer medium volume V_(SET) of the first solar collector 2 ₁.Generally the heat transfer medium volume V_(SET) is a set value for theabove mentioned volume comparison indicating the volume of the heattransfer medium in a specific solar collector 2 ₁, 2 ₂, . . . , 2_(N-1), 2 _(N) and it may vary if the volumes of the solar collectors inthe solar collector arrangement 1 vary. When the measure V_(MEAS) of theheat transfer medium supplied by the circulation pump 11 corresponds tothe heat transfer medium volume V_(SET) of the first solar collector 2₁, the flow control valve 7 in the outflow passage 6 of the first solarcollector 2 ₁ is closed as controlled by the control unit 13 through thecontrol bus CO8 and the respective pilot motor 8.

Next, the portion of the heat transfer medium being in the second solarcollector 2 ₂ and heated therein is started to be collected out of thesecond solar collector 2 ₂. This may take place immediately after theportion of the heat transfer medium being in the first solar collector 2₁ and heated therein is collected out of the first solar collector 2 ₁,or after a certain or an adjustable time period from that. For doingthat the flow control valve 7 in the outflow passage 6 of the secondsolar collector 2 ₂ is opened as controlled by the control unit 13through the control bus CO8 and the respective pilot motor 8, wherebythe portion of the heat transfer medium being in the second solarcollector 2 ₂ and heated therein starts to flow out of the second solarcollector 2 ₂ to the discharge channel 10 through the respective outflowpassage 6 and a portion of the heat transfer medium to be heated issupplied from the feeding channel 9 to the second solar collector 2 ₂through the respective inflow passage 5. After all of the portion of theheat transfer medium heated in the second solar collector 2 ₂ has beencollected out of the second solar collector 2 ₂, the flow control valve7 in the outflow passage 6 of the second solar collector 2 ₂ is closedas controlled by the control unit 13 through the control bus CO8 and therespective pilot motor 8. Similarly as above, when the measure V_(MEAS)of the heat transfer medium supplied by the circulation pump 11corresponds to the heat transfer medium volume V_(SET) of the secondsolar collector 2 ₂, the flow control valve 7 in the outflow passage 6of the second solar collector 2 ₂ is closed as controlled by the controlunit 13 through the control bus CO8 and the respective pilot motor 8.

The procedure disclosed above is repeated as long as the portion of theheat transfer medium being in the last solar collector 2 _(N) of thesolar collector arrangement 1 and heated therein has been collected outof the last solar collector 2 _(N) and replaced with cool portion of theheat transfer medium to be heated in the last solar collector 2 _(N).After that the whole procedure for collecting the heat transfer mediumout of each solar collector 2 ₁, 2 ₂, . . . , 2 ^(N-1), 2 _(N) isrepeated again, either immediately or after a predetermined or anadjustable time period after the portion of the heat transfer mediumbeing in the last solar collector 2 _(N) of the solar collectorarrangement 1 has been collected out of the last solar collector 2 _(N).

In the embodiment disclosed above the heat transfer medium being in thesolar collectors 2 and heated therein is collected out of the solarcollectors 2 one single solar collector 2 at a time. As alreadyindicated above, the heat transfer medium being in the solar collectors2 and heated therein may also be collected out of the solar collectors 2from more than one single solar collector 2 at a time, for example fromsome of the solar collectors 2 of the solar collector arrangement 1 at atime. This embodiment may be used for example in operating conditionswherein the amount of the solar collector energy to be collected is highand therefore the temperature of the heat transfer medium in the solarcollectors 2 increases rapidly.

According to an embodiment the circulation pump 11 and the solarcollector arrangement 1 are operated continuously. This means thatimmediately after the portion of the heat transfer medium being in asolar collector 2 or in some solar collectors 2 and heated thereinhas/have been collected out of the solar collector 2 and replaced withcool heat transfer medium, the portion of the heat transfer medium beingin the following solar collector 2 or in some following solar collectors2 and heated therein will be collected out of that following solarcollector 2 or following solar collectors 2 and replaced with cool heattransfer medium. After the portion of the heat transfer medium being inthe last solar collector 2 _(N) and heated therein has been collectedout of the last solar collector 2 _(N) and replaced with cool heattransfer medium, the procedure for collecting the heated heat transfermedium is started from the beginning again. In this embodiment thecontrol unit 13 is arranged to control the operation of the flow controlvalves 7 and the circulation pump 11 such that the supply flow of theheat transfer medium towards the solar collectors 2 is preferablyadjusted to such an amount that the portion/portions of the heattransfer medium to be supplied to the first solar collector 2 ₁ and topossibly some other solar collectors 2 possibly providing a group ofsolar collectors 2 operating together with the first solar collector 2₁, as disclosed above, has/have enough time to heat up to a maximumachievable temperature by the time the portion/portions of the heattransfer medium being in the last solar collector 2 _(N) and possibly insome other solar collectors 2 possibly providing a group of solarcollectors 2 operating together with the last solar collector 2 _(N),has been collected out of the last solar collector 2 _(N).

An advantage of the latter embodiment of usage of the solar collectorarrangement 1 over the former embodiment of usage is that heated heattransfer medium is supplied constantly to the heat recovery element 12.

The procedures disclosed above are repeated as long as the sun isshining or other circumstances provide that a value of the collectedsolar heat energy is more than operational expenses of the solarcollector arrangement 1.

In the embodiments disclosed above, the portions of the heat transfermedium being in the solar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N)and heated therein are collected out of the solar collectors 2 in turnsone solar collector 2 or some solar collectors 2 at a time in apredetermined order. Alternatively, as disclosed in the followingembodiments, the portions of the heat transfer medium being in the solarcollectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N) and heated therein is tobe collected out of the solar collectors 2 on a basis of the temperatureT_(HTM) of the heat transfer medium in the solar collectors 2 ₁, 2 ₂, .. . , 2 _(N-1), 2 _(N).

For that purpose each solar collector 2 of the solar collectorarrangement 1 may comprise at least one temperature sensor in at leastone collector element 3 for measuring the temperature T_(HTM) of theheat transfer medium in the respective solar collector 2. In thisfurther embodiment, which is schematically disclosed also in FIG. 1,each solar collector 2 comprises two temperature sensors 15U, 15Larranged in the same collector element 3. In its minimum there may beonly one temperature sensor in a single solar collector 2 and in itsmaximum there may be several temperature sensors, i.e. more than twotemperature sensors, in each and every collector element 3 of each solarcollector 2 ₁, 2 ₂, . . . , 2 _(N). 1, 2 _(N) along a longitudinaldirection of the collector element 3.

The temperature sensors 15U in upper parts of the solar collectors 2 ₁,2 ₂, . . . , 2 _(N-1), 2 _(N) are connected to a temperature measurementbus TMU which is further connected to the control unit 13 fortransferring the measured temperature information in the upper parts ofthe solar collectors 2 to the control unit 13. The temperature sensors15L in lower parts of the solar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2_(N) are connected to a temperature measurement bus TML which is furtherconnected to the control unit 13 for transferring the measuredtemperature information in the lower parts of the solar collectors 2 tothe control unit 13.

According to an embodiment the portions of the heat transfer mediumbeing in the solar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N) arecollected out of the solar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N)one solar collector 2 at a time or some solar collectors 2 at a time inan order determined by the temperatures T_(HTM) of the portions of theheat transfer medium in the solar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1),2 _(N). In this embodiment it is set into the control unit 13 a targetvalue T_(SET) for the temperatures T_(HTM) of the portions of the heattransfer medium in the solar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2_(N) so that after the temperature T_(HTM) of the portion of the heattransfer medium in the solar collector 2 ₁, 2 ₂, . . . , 2 _(N-1), 2_(N) has reached the set target value T_(SET) in a specific solarcollector 2 or in some collectors 2, the portion/portions of the heattransfer medium is collected out of that specific solar collector 2 orout of the specific solar collectors 2 and replaced by a portion of coolheat transfer medium supplied into that specific solar collector 2 orthe specific solar collectors 2. The temperature T_(HTM) of the portionof the heat transfer medium to be compared with the set target valueT_(SET) may for example be the highest single value of the measuredtemperatures of the portion of the heat transfer medium provided by thetemperature sensors 15U, 15L, or the lowest single value of the measuredtemperatures of the portion of the heat transfer medium provided by thetemperature sensors 15U, 15L or an average value of the temperatures ofthe portion of the heat transfer medium provided by the temperaturesensors 15U, 15L. The target value T_(SET) may be set according to knownoperating characteristics of the solar collectors 2, for example.

In the arrangement disclosed in the preceding paragraph the portion ofthe heat transfer medium in the solar collector 2 is collected out ofthe solar collector(s) 2 after the temperature T_(HTM) of the portion ofthe heat transfer medium in the solar collector(s) 2 has/have reachedthe set target value T_(SET). The portions of the heat transfer mediumare collected out of the solar collectors 2 of the solar collectorarrangement 1 in that order according to which order the portions of theheat transfer medium in different solar collectors 2 have reached theset target value T_(SET), but so that the heat transfer medium is stillcollected out of only one solar collector or some solar collectors at atime. In an ideal situation, wherein heat conduction properties andenvironmental characteristics of all the solar collectors 2 in the solarcollector arrangement 1 are same, the order the portions of the heattransfer medium are to be collected out of the solar collectors 2 is inpractice the same all the time. Also the circulation pump 11 may then beon and being operated continuously, whereby heated heat transfer mediummay be supplied continuously to the heat recovery element 12.

According to an embodiment the solar collector arrangement 1 comprises aweather station 16 connected to the control unit 13, the weather station16 comprising at least one temperature sensor for measuring airtemperature T_(AM) at the location of the solar collector arrangement 1.On the basis of the measured air temperature T_(AM) at the location ofthe solar collector arrangement 1 the control unit 13 may determine thesettable target value T_(SET) for the temperature T_(HTM) of the heattransfer medium in the solar collectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2_(N). The weather station 16 may also comprise additional sensors formeasuring other properties of the air at the location of the solarcollector arrangement 1, such as humidity of air and wind velocity,which may also be used when the target value T_(SET) for the temperatureT_(HTM) of the heat transfer medium in the solar collectors 2 ₁, 2 ₂, .. . , 2 _(N-1), 2 _(N) is to be determined.

According to an embodiment the solar collector arrangement 1 comprises aserver unit 17 connected to the control unit 13, the server unit 17providing a connection to a weather forecast service providing a weatherforecast for a region of the location of the solar collector arrangement1. The weather forecast may provide at least an estimate for airtemperature T_(AF) in the region of the location of the solar collectorarrangement 1. On the basis of the forecasted air temperature T_(AF) atthe location of the solar collector arrangement 1 the control unit 13may determine the settable target value T_(SET) for the temperatureT_(HTM) of the heat transfer medium in the solar collectors 2 ₁, 2 ₂, .. . , 2 _(N-1), 2 _(N). The weather forecast may also compriseadditional information about other properties of the air for thelocation of the solar collector arrangement 1, such as humidity of airand wind velocity, which may also be used when the target value T_(SET)for the temperature T_(HTM) of the heat transfer medium in the solarcollectors 2 ₁, 2 ₂, . . . , 2 _(N-1), 2 _(N) is to be determined.

In the embodiments of the solar collector arrangement 1 comprisingeither the weather station 16 or the server 17 the settable target valueT_(SET) to be set for the temperature T_(HTM) of the heat transfermedium in the solar collectors 2 may be set according to the measuredair temperature T_(AM) or the forecasted air temperature T_(AF) at thelocation of the solar collector arrangement 1. In this application thecontrol unit 13 may comprise a learning module 13LM for providing alearning phase which determines the dependency between the measured airtemperature T_(AM) at the location of the solar collector arrangement 1and the achieved temperature T_(HTM) of the heat transfer medium in thesolar collectors 2 or between the forecasted air temperature T_(AF) atthe location of the solar collector arrangement 1 and the achievedtemperature T_(HTM) of the heat transfer medium in the solar collectors2. The control unit 13 may also comprise an optimization module 13OM forproviding an optimization phase which determines a number of, i.e. atleast one, control strategies for controlling operation of the flowcontrol valves 7 on the basis of the dependency between the measured airtemperature T_(AM) or the forecasted air temperature T_(AF) at thelocation of the solar collector arrangement 1 and the achievedtemperature T_(HTM) of the heat transfer medium in the solar collectors2, as determined above.

FIG. 2 shows schematically an internal assembly and operation of thecontrol unit 13 of the solar collector arrangement. The control unit 13comprises a processor unit 13PU which provides necessary calculation,determination and control operations needed for controlling theoperation of the solar collector arrangement 1. For providing thoseoperations the processor unit 13PU comprises a dedicated softwareimplementing those operations.

The control unit 13 comprises also the learning module 13LM, which maybe internal or external to the processor unit 13PU, in FIG. 2 it isshown to be external to the processor unit 13PU. As said above, thelearning module 13LM is arranged to determine the dependency between themeasured air temperature T_(AM) at the location of the solar collectorarrangement 1 and the achieved temperature T_(HTM) of the heat transfermedium in the solar collectors 2 or between the forecasted airtemperature T_(AF) at the location of the solar collector arrangement 1and the achieved temperature T_(HTM) of the heat transfer medium in thesolar collectors 2.

The learning module 13LM provides the learning phase, whereby thecontrol unit 13 receives the measured air temperature T_(AM) or theforecasted air temperature T_(AF) at the location of the solar collectorarrangement 1 and stores that temperature to a comparison tabledisclosed schematically in the left hand side column of FIG. 3. Thecomparison table may be maintained in the learning module 13LM. Themeasured T_(AM) or forecasted T_(AF) air temperature may be the highesttemperature for a day, or the highest temperature for an hour in theday, whereby the comparison table may be determined as a daily basis oran hourly basis, for example.

For determining the dependency between the measured air temperatureT_(AM) at the location of the solar collector arrangement 1 and theachieved temperature T_(HTM) of the heat transfer medium in the solarcollectors 2 or between the forecasted air temperature T_(AF) at thelocation of the solar collector arrangement 1 and the achievedtemperature T_(HTM) of the heat transfer medium in the solar collectors2, the control unit 13 receives also the achieved measured temperatureT_(HTM) of the heat transfer medium in the solar collectors 2corresponding to the respective measured air temperature T_(AM) or theforecasted air temperature T_(AF) at the location of the solar collectorarrangement 1. The control unit 13 stores the measured temperatureT_(HT)M of the heat transfer medium in the solar collectors 2 in theright hand side column in the comparison table at a point correspondingto the respective measured air temperature T_(AM) or the forecasted airtemperature T_(AF) at the location of the solar collector arrangement 1.The comparison table thus determines or presents the dependency betweenthe measured T_(AM) or the forecasted T_(AF) temperature and theachieved temperature T_(HTM) of the heat transfer medium in the solarcollectors 2. The achieved temperature T_(HTM) of the heat transfermedium in the solar collectors 2 may be used in the further operation ofthe solar collector arrangement 1 as target set value T_(SET) for thetemperature T_(HTM) of the heat transfer medium in the solar collectors2 of the solar collector arrangement 1.

The control unit 13 comprises also the optimization module 13OM, whichmay be internal or external to the processor unit 13PU, in FIG. 2 it isshown to be external to the processor unit 13PU. As said above, theoptimization module 13LM is arranged to determine at least one controlstrategy for controlling operation of the flow control valves 7 on thebasis of the dependency between the measured air temperature T_(AM) orthe forecasted air temperature T_(AF) at the location of the solarcollector arrangement 1 and the achieved temperature T_(HTM) of the heattransfer medium in the solar collectors 2.

In the optimization phase the control unit 13 in co-operation with thelearning module 13LM and the optimization module 13OM therein comparesthe measured temperature T_(HTM) of the heat transfer medium in thesolar collectors 2 to the temperature values presented in thetemperature comparison table and controls the operation of the flowcontrol valves 7 accordingly. For example according to an embodiment, ifthe measured air temperature T_(AM) or the forecasted air temperatureT_(AF) at the location of the solar collector arrangement 1 is 19degrees of Celsius and the respective expected temperature T_(HTM) ofthe heat transfer medium in the solar collectors 2 is 79 degrees ofCelsius, the control unit 13 provides a control operation to open theflow control valve 7 of the solar collector 2 after the temperaturesensors 15U, 15L indicate that the temperature T_(HTM) of the heattransfer medium in that solar collector 2 has reached the value 79degrees of Celsius. Other kind of control strategies may, however beapplied for controlling the operation of the solar collector arrangement1.

According to an embodiment of the solar collector arrangement 1comprising the temperature sensors 15U, 15L in the solar collectors 2,the control unit 13 is arranged to determine the second derivative, i.e.the second differential coefficient, d²T_(HTM)/dt² of the temperatureT_(HTM) of the heat transfer medium in the solar collectors 2. Thesecond derivative d²T_(HTM)/dt² of the temperature T_(HTM) of the heattransfer medium indicates the speed of the change of the temperatureT_(HTM) of the heat transfer medium in the solar collector 2 asdetermined on the basis of at least two successive temperature T_(HTM)measurements of the heat transfer medium. Each solar collector 2 may beconsidered separately. When the second derivative d²T_(HTM)/dt² ispositive, it means that the heat transfer medium being in the solarcollector 2 receives heat with an increasing speed, i.e. more heat in apredetermined time period is received by the heat transfer medium beingin the solar collector 2. When the second derivative d²T_(HTM)/dt²becomes negative, it means that the heat transfer medium being in thesolar collector 2 receives heat with a decreasing speed, i.e. less heatin a predetermined time period is received by the heat transfer mediumbeing in the solar collector 2. When the second derivative d²T_(HTM)/dt²becomes negative, it means that the capability of the heat transfermedium in the solar collector to receive more heat is about to end andit may be more productive in view of the heat collection to collect theheated heat transfer medium out of the solar collector 2 and to fill thesolar collector 2 with cool heat transfer medium to be heated althoughthe portion of the heat transfer medium being in the solar collector 2and heated therein has not yet received the target temperature T_(SET)set for the temperature T_(HTM) of heat transfer medium in the solarcollector 2.

The determination of the second derivative d²T_(HTM)/dt² of thetemperature T_(HTM) of the heat transfer medium may be applied inconnection with any embodiment disclosed above. FIG. 2 disclosesschematically also an operation module for the determination of thesecond derivative d²T_(HTM)/dt² of the temperature T_(HTM) of the heattransfer medium. The operation module for the determination of thesecond derivative may be internal or external to the processor unit13PU, in FIG. 2 it is shown to be external to the processor unit 13PU.

In the solution and its embodiments disclosed above the heat transfermedium heated in the solar collectors is collected out of the solarcollectors one collector or some solar collectors at a time. This meansfor example that the portion of the heat transfer medium heated in asingle solar collector may be collected out of that solar collectorimmediately after the heat transfer medium has reached an assumed or aset target temperature for the heated heat transfer medium although theportions of the heat transfer medium in the other solar collectors havenot yet reached the target temperature.

According to an embodiment the solar collector arrangement 1 may be usedduring a winter to melt away snow collected on top of the solarcollectors 2. This takes place by feeding warm heat transfer medium fromthe heat recovery element to the solar collectors 2 through the feedingchannel 9, whereby the warm heat transfer medium heats the solarcollectors 2 and melts the snow away. A reason for melting the snow awaymay be to reduce a total weight provided by the snow and the solarcollectors 2, thus reducing stresses directed to a structure of a roof.In that embodiment of usage for melting the snow the arrangement isoperated only when it is snowing—it does not need to be operated all thetime. Another reason for melting the snow away may be to remove the snowearly in a spring from the top of the solar collectors so that the solarheat energy may be started to be utilized as soon as the sun willprovide enough heat energy after the winter. In that embodiment of usagefor melting the snow the arrangement may be operated only once at a timewhen the snow is intended to be removed from the top of the solarcollectors 2. The feed of warm heat transfer medium to the solarcollectors 2 for melting the snow may also be utilized in other kind ofsolar collector arrangement than the solar collector arrangementsdisclosed above.

It will be obvious to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The invention and its embodiments are not limited to the examplesdescribed above but may vary within the scope of the claims.

1. A solar collector arrangement comprising at least two solarcollectors, each solar collector comprising at least one collectorelement with at least one flow channel for receiving heat transfermedium to be heated in the solar collector, at least one inflow passagefor allowing a flow of the heat transfer medium to be heated into the atleast one flow channel and at least one outflow passage for allowing aflow of heat transfer medium heated in the solar collector out of the atleast one flow channel, and in which arrangement the at least two solarcollectors are arranged in parallel connection relative to each otherand the heat transfer medium to be heated in the solar collectors andthe heat transfer medium heated in the solar collectors are arranged toflow into the solar collectors and out of the solar collectors in turnsone solar collector or some solar collectors of the solar collectorarrangement at a time.
 2. A solar collector arrangement as claimed inclaim 1, wherein the solar collector arrangement comprises a feedingchannel for feeding the heat transfer medium to be heated into the solarcollectors, a discharge channel for collecting the heat transfer mediumheated in the solar collectors out of the solar collectors, and whereinthere is a controllable flow control valve in the outflow passage ofeach solar collector for controlling the connection of the outflowpassage of the solar collector to the discharge channel, and wherein oneflow control valve or some flow control valves is/are arranged to becontrolled at a time for controlling the flow of the heat transfermedium to be heated into the solar collectors and the flow of the heattransfer medium heated in the solar collectors out of the solarcollectors one solar collector or some solar collectors at a time.
 3. Asolar collector arrangement as claimed in claim 1, wherein the solarcollector arrangement comprises a control unit configured to control anorder of connecting the solar collectors to the discharge channel inturns one solar collector or some solar collectors at a time.
 4. A solarcollector arrangement as claimed in claim 3, wherein the control unit isarranged to control the flow control valve of one solar collector orsome solar collectors at a time for connecting the outflow passage ofone solar collector or some solar collectors to the discharge channel ata time.
 5. A solar collector arrangement as claimed in claim 1, whereinthe outflow passages of the solar collectors of the solar collectorarrangement are connected to the discharge channel one solar collectoror some solar collectors at a time in a predetermined order.
 6. A solarcollector arrangement as claimed in claim 1, wherein the solar collectorcomprises at least one temperature sensor for measuring temperature ofthe heat transfer medium in the at least one flow channel in the solarcollector, and wherein the solar collectors of the solar collectorarrangement are connected to the discharge channel in an orderdetermined on a basis of measured temperatures of the heat transfermedium in the solar collectors.
 7. A solar collector arrangement asclaimed in claim 6, wherein a control unit of the solar collectorarrangement comprises at least one settable target value for thetemperature of the heat transfer medium in the solar collector, andwherein the heat transfer medium is to be collected out of the solarcollector to the discharge channel in response to the temperature of theheat transfer medium in the solar collector receiving the target valueset for the temperature of the heat transfer medium in the solarcollector.
 8. A solar collector arrangement as claimed in claim 7,wherein the solar collector arrangement comprises at least one serverunit arranged in connection with a weather forecast service and that thesettable target value for the temperature of the heat transfer medium inthe solar collector is set on the basis of the forecasted temperaturefor a region of a location of the solar collector arrangement.
 9. Asolar collector arrangement as claimed in claim 8, wherein the controlunit comprises a learning unit for describing a dependency between theforecasted air temperature and the respective temperature of the heattransfer medium to be achieved in the solar collector, and wherein thecontrol unit comprises an optimization unit for controlling theoperation of the flow control valves of the solar collectors on thebasis of the temperature dependency between the forecasted airtemperature and the respective temperature of the heat transfer mediumto be achieved in the solar collectors.
 10. A solar collectorarrangement as claimed in claim 6, wherein a control unit of the solarcollector arrangement is arranged to determine a second derivate of thetemperatures of the heat transfer medium in the solar collectors andthat the control unit is arranged to control the flow control valves ofthe solar collectors for collecting the heat transfer medium heated inthe solar collectors out of the solar collectors in response to thesecond derivate of the temperature of the heat transfer medium in thesolar collector being negative.
 11. A method of operating a solarcollector arrangement comprising at least two solar collectors arrangedin parallel connection relative to each other, each solar collectorcomprising at least one collector element with at least one flow channelfor receiving heat transfer medium to be heated in the solar collector,at least one inflow passage for allowing a flow of the heat transfermedium to be heated into the at least one flow channel and at least oneoutflow passage for allowing a flow of heat transfer medium heated inthe solar collector out of the at least one flow channel, the methodcomprising controlling the flow of the heat transfer medium to be heatedin the solar collectors into the solar collectors and the flow of theheat transfer medium heated in the solar collectors out of the solarcollectors in turns one solar collector or some solar collectors of thesolar collector arrangement at a time.
 12. A method as claimed in claim11, comprising feeding the heat transfer medium to be heated in thesolar collectors into the solar collectors through a feeding channel,collecting the heat transfer medium heated in the solar collectors outof the solar collectors through a discharge channel, and controllingcontrollable flow control valves arranged in the outflow passages of thesolar collectors one flow control valve or some flow control valves at atime for controlling the flow of the heat transfer medium to be heatedinto the solar collectors and the flow of the heat transfer mediumheated in the solar collectors out of the solar collectors one solarcollector or some solar collectors at a time.
 13. A method as claimed inclaim 11, comprising controlling an order of connecting the solarcollectors to the discharge channel in turns one solar collector or somesolar collectors at a time by a control unit of the solar collectorarrangement.
 14. A method as claimed in claim 13, comprising controllingby the control unit the flow control valve of one solar collector orsome solar collectors at a time for connecting the outflow passage ofone or some solar collectors to the discharge channel at a time.
 15. Amethod as claimed in claim 11, comprising connecting the outflowpassages of the solar collectors to the discharge channel one solarcollector or some solar collectors at a time in a predetermined order.16. A method as claimed in claim 11, comprising measuring temperature ofthe heat transfer medium in the at least one flow channel in the solarcollector and connecting the solar collectors of the solar collectorarrangement to the discharge channel in an order determined on a basisof measured temperatures of the heat transfer medium in the solarcollectors.
 17. A method as claimed in claim 16, comprising setting atleast one settable target value for the temperature of the heat transfermedium in the solar collector, and collecting the heat transfer mediumout of the solar collector to the discharge channel in response to thetemperature of the heat transfer medium in the solar collector receivingthe target value set for the temperature of the heat transfer medium inthe solar collector.
 18. A method as claimed in claim 17, comprisingarranging the solar collector arrangement in connection with a weatherforecast service and setting the settable target value for thetemperature of the heat transfer medium in the solar collector on thebasis of the forecasted temperature for a region of a location of thesolar collector arrangement.
 19. A method as claimed in claim 18,comprising providing in the control unit a learning unit for describinga dependency between the forecasted air temperature and the respectivetemperature of the heat transfer medium to be achieved in the solarcollector, and providing in the control unit an optimization unit forcontrolling the operation of the flow control valves of the solarcollectors on the basis of the temperature dependency between theforecasted air temperature and the respective temperature of the heattransfer medium to be achieved in the solar collectors.
 20. A method asclaimed in claim 16, comprising determining a second derivate of thetemperatures of the heat transfer medium in the solar collectors andcontrolling the flow control valve of the solar collector for collectingthe heat transfer medium heated in the solar collector out of the solarcollector in response to the second derivate of the temperature of theheat transfer medium in the solar collector being negative.